Leveraging Large Deformation Finite Element (LDFE) Modelling to Support Jack-Up Site Acceptance Assurance at a 97 Meter Water Depth Site with Marginal Leg Reserve

Abstract Developing marginal gas fields where economic viability hinges on the ability to drill using a jack-up rig in combination with a wellhead platform (WHP) can be highly cost-effective. However, this approach becomes challenging at locations with water depths approaching 98 m, where jack-up leg length may be insufficient due to deep spudcan penetration in soft soils. Accurate penetration prediction is therefore critical to ensure safe operations and avoid costly mitigations such as rig or platform modifications. To address this challenge, a Large Deformation Finite Element (LDFE) analysis using the Coupled Eulerian–Lagrangian (CEL) technique was performed to simulate spudcan–soil interaction under site-specific conditions. The CEL approach, implemented in ABAQUS/CAE, enables realistic modelling of continuous penetration by allowing soil to flow through a fixed mesh, overcoming distortion issues common in traditional methods. The spudcan was modelled as a rigid body, and the soil domain comprised approximately 450,000 elements with refined meshing near the spudcan. A lower-bound soil strength profile was adopted to conservatively estimate maximum penetration. The simulation predicted a spudcan tip penetration of 27.8 m at a preload of 113.4 MN, confirming sufficient leg length to achieve the required air gap without modifications. Field measurements during installation showed actual penetration of 27.5 m at 110 MN, closely matching the numerical prediction. This strong correlation validated the model's reliability and provided critical assurance for the project team. By reducing geotechnical uncertainty and improving confidence in jack-up performance, the advanced modelling approach enabled the adoption of a cost-effective development concept, avoided unnecessary mitigations, and safeguarded project cost and schedule.